CROPPERS wondering how much canola to grow this season - if any - have been advised the beet western yellows virus risk is not likely to be as high as last year.
That is according to SARDI pathologist Jenny Davidson, who said a "perfect storm" of environmental conditions, plus a lack of knowledge on the virus, contributed to the prolific outbreak last season.
The guest speaker at the recent Mallee Sustainable Farming tri-state forum at Pinnaroo, said there was no "silver bullet" to completely get rid of green peach aphid - the main carrier of the virus - but intense frosts last winter and spring meant aphid populations had "absolutely crashed".
"Really we are back to square one," she said.
The perfect agronomic storm leading up to the outbreak, included two extensive summer rainfall events last January, that had set up a large green bridge.
"This allowed the aphid to multiply prior to and after sowing," she said.
"Then we had subtropical conditions in May and early June, which was the clincher.
"In those environmental conditions, the aphid population can multiply rapidly and transfer the virus astronomically."
Advising against complacency fellow plant pathologist Frank Henry, from the Victorian Department of Economic Development, Jobs, Transport and Resources, says farmers need to be on the lookout for aphids.
"It is advisable you get a good knockdown of weeds at least two weeks prior to sowing, because weeds will host GPAs and BWYV," he said.
Ms Davidson said "almost any broadleaf plant could become infected by the virus, plus pulse crops, brassicas, lucerne, medics, clover and leafy vegetables".
"Weeds such as wild radish, marshmallow, wild turnip, fleabane, nightshade, stinkweed, thistles, bedstraw and muskweed can also host the virus," she said.
Ms Davidson said one bonus was that the virus was restricted to the phloem of the plant, in the sap area, so it did not affect the seed.
"So it can't transfer over from last year's seed," she said.
Studies undertaken in 2104 also showed that other than good weed control, good in-paddock management included standing stubble, thicker crops and seed dressings.
Mr Henry said neo-nicotinoide seed treatments were critical in controlling the aphids, but farmers needed to be stringent on their instructions because of the threat to bee populations if used "off-label".
He said there were severe infestations of the virus last year on canola not treated with Gaucho or Cruiser Opi neo-nicotinoide-based seed dressing.
"Many of the canola problems with insects occur at emergence so seed dressings are recommended, and then an in-season application of Transform (sulfoxaflor) insecticide is the best control of GPAs, if required," Mr Henry said.
"GPAs are resistant to synthetic pyrethroid and carbamates insecticides," she said.
"Transform is recommended, because it was the only registered foliar insecticide that was shown to be effective in 2014, but don't just rely on Transform.
"If other aphids like the cabbage or turnip aphid are identified in-crop, try to rotate your insecticides so to not to build up resistance."
Alisha Fogden
Cropping editor of Stock Journal.
Cropping editor of Stock Journal.
